Guide Wave Long Range Ultrasonic Testing
GW LRUT - Advance NDT Service
Long Range Ultrasonic testing (LRUT) also known as Guided Wave Ultrasonic Testing (GWUT) is an Ultrasonic method wherein ultrasonic waves are transmitted along the pipe wall (guiding walls) up to 180meters in length.
GW LRUT – Guided Wave Long Range Ultrasonic testing is a rapid screening test method for integrity assessment of pipelines, non-piggable buried, encased piping, vertical or inaccessible piping (e.g. overhead pipe racks) or epoxy coated pipelines to locate areas of potential degradation or engineering concerns and gross discontinuities for targeted assessment and inspection. While conventional NDT test methods provide localized inspection, underneath or in the vicinity of the sensors, LRUT is able to test 100% circumferential wall over tens of meters of the pipe length from the single inspection (contact point) location.
Guided Wave LRUT is used to inspect 100% of pipe circumference along the pipe length from a single location. Low frequency (15-85kHz) torsional or longitudinal guided waves are generated into the pipe body (360 degrees all around the pipe circumference) on both sides of the transducer assembly collar. These ultrasonic waves propagate in the axial direction of the pipe until the entire energy is attenuated or dissipated.
When these guided waves intercepts areas of change in cross section such as butt welds, pipe supports, elbows, flanges or gross discontinuities such as severe corrosion, erosion, pitting clusters, etc; they reflect laminar waves back to the sensors at the location of wave initiation (Transducer assembly Collar). Multiple frequency signals are acquired simultaneously and analysed. The time-of-flight for each reflection and its dominant frequency is analysed to determine its location from the sensor.
The quadrants determine the feature’s circumferential position on the pipe wall. The amplitude of the signal determines the significance of the defect in relative loss of cross section (LCS). The minimum LCS (loss of cross sectional area) that can be currently confidently detected is 3% of the total cross sectional area of the pipe under examination.
Guided Wave LRUT is primarily applied on pipelines having limited access or only localised access; to avoid unnecessary excavation, coating removal or scaffolding installation. The use of LRUT significantly reduces maintenance costs and is a perfect inspection method for unpiggable pipes or inaccessible pipe sections. LRUT can be used on pipe diameters ranging from 38mm (1.5”) to 1200mm (48”) to detect loss of cross section (LSC) or areas of concern such as corrosion or erosion pockets around the pipe’s circumference.
The sensitivity of the LRUT is typically 2.5% LSC, equally sensitive on both ID and OD of the pipe. Absolute defect size will depend on the pipe size (for large ODs and wall thickness, 5% can be a penetrating defect). The signal amplitude will depend on the shape of a discontinuity e.g. extended area over the circumference or the extended depth in the wall.
LRUT can be performed on in-service pipelines operating in the range of 0°C to 70°C. Testing can be done at higher temperatures and as low as -30°C but with exceptional risk management plans. Moreover, LRUT can be applied on various materials and different pipe diameters having wall thickness up to 40mm.